The overall aim of this work is to understand how the growth of the adult pancreas is regulated to provide an adequate supply of digestive enzymes. We hypothesize that growth can occur by two mechanisms. The first occurs in response to diet and hormones and involves stimulation of differentiated acinar cells to enter the cell cycle and divide. The second form of growth that occurs following tissue injury such as pancreatitis involves dedifferentiation, cell division and dedifferentiation and will be referred to as regeneration. Our primary model for hormonal stimulation of growth involves feeding the synthetic protease inhibitor, camostat to mice to increase plasma CCK. We have shown this growth requires the calcium activated phosphates calcineurin and the mTOR pathway, and is accompanied by the activation of the MAP kinases, ERK and JNK, and the expression of a number of early response genes including multiple c-Jun and c-Fos family members. In Specific Aim 1 we will study the mechanisms mediating mitogenesis and growth of differentiated cells driven by chronic CCK elevation. a) We will identify the cell cycle regulators activated by CCK. b) We will study target genes regulated by NFATs (regulated by calcineurin) and AP-1 (activated by MAP kinases) with particular attention to regulation of cell-cycle regulating genes such as cyclin D1 and PCNA and to endogenous feedback inhibitors such as MClP1 for calcineurin. In Specific Aim 2 we will determine the mechanisms mediating regeneration after tissue injury. We will study regeneration following two models of pancreatitis induced by ethionine and caerulein over-stimulation. a) We will determine how the pattern of gene expression is altered in regeneration in the presence and absence of CCK using CCK deficient mice. b) We will determine the importance of calcineurin and mTOR for regeneration using both pharmacological inhibitors and gene targeted mice. In Specific Aim 3 we will determine the regulatory mechanisms for CCK and Growth Factor stimulated growth of acinar cells in primary monolayer culture which serves as a model for growth similar to regeneration and in which proteins and siRNA can be expressed with adenoviral vectors. We will first characterize the dedifferentiation and establish the acinar cell origin of dividing cells by lineage tracing. We will then evaluate the importance of different signaling pathways and cell cycle components with a focus on the key role of c-jun and AP1. Overall, the project will lead to better understanding of pancreatic growth and assist in designing approaches to regulating pancreatic growth in humans.